Certain 4H-substituted-1,2,4-triazoles such as Indar.RTM. fungicide are known to possess fungicidal activity. Indar.RTM. fungicide, 4H-n-butyl-1,2,4-triazole is particularly effective against wheat leaf rust. This activity is reported in Science, Vol. 169, pages 997 and 998, Sept. 4, 1970 by William C. von Meyer. Various methods for preparing 4H-substituted-1,2,4-triazoles have been reviewed in K. T. Potts' article in "Chemical Reviews" Vol. 61, pages 87 to 127, 1961; in R. K. Bartlett and I. R. Humphrey's article in "Journal of the Chemical Society" (London) page 1664 to 1666, 1967; in "Chemical Abstracts" Vol. 77, 34431w, 1972; in "Chemical Abstracts" Vol. 77, 34426y, 1972 and in "Chemical Abstracts" Vol. 85, 123928w, 1976. An article in "Russian Chemical Reviews", Vol. 43 (9), page 795 to 804, 1974 by A. L. Rusanov discloses the preparation of 4H-amino-1,2,4- triazoles by the reaction of 2 moles of a substituted nitrile with one mole of hydrazine.
The current process for the production of 4H-n-butyl-1,2,4-triazole, a commercial fungicide sold by Rohm and Haas Company under the trademark Indar.RTM. utilizes a three step process wherein the triazole ring carbon atoms are derived from methyl formate and triethyl orthoformate. In this process formylhydrazine is formed from hydrazine hydrate and methyl formate. This formylhydrazine is then reacted in situ with triethyl orthoformate to give N-ethoxymethylene-N'-formylhydrazine. Addition of n-butylamine followed by heating for several hours produces high purity 4H-n-butyl-1,2,4-triazole in better than 70% yields. The major difficulty with this process is that the final product obtained has a relatively high net selling price. This is due primarily to unusually high raw material costs which, in turn, are a direct result of the inefficient use of the expensive starting material, triethyl orthoformate as the source of one of the carbon atoms of the triazole ring. This reagent alone accounts for about 50% of the total raw material costs for this product. This is due to the fact that less than 10% of the weight of the triethyl orthoformate initially charged ends up in the final product. Thus there is a need to reduce both the raw material cost and the net selling price for the manufacture of 4H-substituted 1,2,4-triazoles by replacing triethyl orthoformate with a more efficient and less expensive reagent to provide the source of the triazole ring carbon atoms. The process of the present invention meets these requirements and further allows for symmetrical substitution in the 3 and 5 positions of the triazole ring.